基于流固耦合热障涂层涡轮叶片应力场的数值模拟

发布时间：2018-06-23 02:32

本文选题：热障涂层 + 流固耦合　；参考：《湘潭大学》2015年硕士论文

【摘要】：热障涂层因其良好的高温隔热效果而广泛应用于航空发动机涡轮叶片,但是涂层在服役过程中的剥离失效严重制约了航空发动机的使用寿命。因此,认识热障涂层的破坏失效机理对于提高叶片使用寿命尤为重要。高温环境与应力集中是涂层内裂纹萌生和扩展的根本原因。本文采用流固耦合的方法计算得到热障涂层涡轮叶片服役过程中温度和应力分布,主要研究内容和结果如下:(1)本文建立了热障涂层涡轮叶片流固耦合理论模型,流体域湍流核心区解时均化的N-S方程,壁面边界层不直接求解微分方程而是用半经验公式模拟近壁区温度、速度等物理变量。固体域采用共轭热传导理论求解温度场,将温度场作为预定义场变量,利用热弹塑性理论求解固体域应力场。耦合边界处温度和热流连续。(2)本文实现了热障涂层流固耦合的数值模拟过程,流体模型和固体模型分别采用FLUENT软件和ABAQUS软件单独进行计算,耦合界面通过MPCCI实现温度和对流换热系数等物理变量的数据传递。ABAQUS软件中利用布尔相减和布尔相加技术建立多层复杂几何结构的二维热障涂层几何模型,网格划分过程中,靠近氧化层附近区域采用四边形为主、三角形为辅的网格策略,给定位移和热边界,建立固体域计算模型。本文流体域采用ICEM CFD软件进行结构化网格划分,考虑边界层物理变量梯度效应,加密边界层附近网格密度。为了实现流体和固体之间的共轭热传导,固体域传递壁面温度到流体模型,反过来流体域传递膜温度和对流换热系数到固体域,当固体域和流体域计算收敛后,计算结束。(3)本文计算得到了二维热障涂层涡轮叶片服役过程中的温度和应力分布:稳态条件下,陶瓷层表面前缘和尾缘处温度相对较高,温度最大值为1035°C,位于叶片前缘处,吸力面温度整体低于压力面温度。另外,镧系氧化物面层(LCO)有一定的隔热效果,可以使金属基底温度下降20°C左右。发动机稳定工作阶段,叶片氧化层环向应力值分布在1.12GPa~3.75 GPa之间,吸力面和压力面氧化层内应力水平高,容易引起裂纹的萌生与扩展;叶片冷却后,氧化层内环向残余应力值分布在250 MPa~-3.5 GPa之间,前缘和尾缘附近残余应力水平高,容易引起应力集中。总之,本文采用流固耦合分析方法实现了二维热障涂层涡轮叶片瞬态温度场和应力场的数值模拟,得到各个时间段热障涂层涡轮叶片温度和热应力的分布,对叶片服役过程中可能出现的失效位置做了初步的预测,为热障涂层的研究提供了一种新的思路。
[Abstract]:Thermal barrier coatings are widely used in aero-engine turbine blades due to their good thermal insulation effect. However, the service life of aero-engine is seriously restricted by the peeling failure of the coatings in service. Therefore, it is very important to understand the failure mechanism of thermal barrier coating for increasing the service life of blade. High temperature environment and stress concentration are the root causes of crack initiation and propagation. In this paper, the temperature and stress distribution of thermal barrier coating turbine blade during service is calculated by using fluid-solid coupling method. The main contents and results are as follows: (1) the theoretical model of fluid-solid coupling of thermal barrier coating turbine blade is established in this paper. The homogeneous N-S equation in turbulent core region in fluid domain is not directly solved by the wall boundary layer, but by semi-empirical formula to simulate the physical variables such as temperature and velocity near the wall. The conjugate heat conduction theory is used to solve the temperature field and the temperature field is taken as the predefined field variable. The thermoelastic-plastic theory is used to solve the stress field in the solid domain. The coupled boundary temperature and heat flux are continuous. (2) the numerical simulation process of fluid-solid coupling of thermal barrier coating is realized. The fluid model and solid model are calculated separately by fluent and Abaqus software. The coupled interface realizes the data transfer of physical variables such as temperature and convection heat transfer coefficient by MPCCI. In Abaqus software, using Boolean subtraction and Boolean addition techniques, a two-dimensional thermal barrier coating geometric model with multilayer and complex geometry structure is established. The meshing strategy of quadrilateral and triangle is used in the area near the oxide layer. The calculation model of solid domain is established based on the given displacement and thermal boundary. In this paper, ICEM CFD software is used for structured mesh generation in the fluid domain. Considering the gradient effect of physical variables in the boundary layer, the density of the grid near the boundary layer is encrypted. In order to realize the conjugate heat conduction between fluid and solid, the solid domain transfers wall temperature to the fluid model, in turn, the fluid domain transfer membrane temperature and convection heat transfer coefficient to the solid domain, when the calculation in the solid and fluid domains converges, (3) in this paper, the temperature and stress distribution of two-dimensional thermal barrier coated turbine blade are calculated. Under steady state condition, the temperature at the front edge and tail edge of ceramic layer is relatively high, and the maximum temperature is 1035 掳C, which is located at the front edge of the blade. Suction surface temperature is lower than pressure surface temperature. In addition, the lanthanide oxide surface layer (LCO) has a certain thermal insulation effect, which can reduce the metal substrate temperature by about 20 掳C. In the stable working stage of the engine, the circumferential stress of the oxidation layer of the blade is between 1.12 GPA and 3.75 GPA, and the stress level of the oxidation layer on the suction and pressure surfaces is high, which can easily lead to the initiation and propagation of cracks, and when the blade is cooled, The internal circumferential residual stress of the oxide layer is distributed between 250 MPA and 3.5 GPA, and the residual stress level near the front edge and the tail edge is high, which can easily lead to stress concentration. In a word, the numerical simulation of transient temperature field and stress field of two dimensional thermal barrier coating turbine blade is realized by using fluid-solid coupling analysis method, and the distribution of temperature and thermal stress of thermal barrier coating turbine blade is obtained in every time period. The failure locations of the blades during service are preliminarily predicted, which provides a new idea for the study of thermal barrier coatings.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：V263

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